The Commentary on Sefer Yeṣira (Book of Creation), with its pronounced Pythagorean
and Neo-Platonic overtones, written by Saadya Gaon in 931, stands out among the
other writings of this Jewish theologian (mutakallim), and raises the question of
the purpose of its composition. It has been argued that in writing a commentary
on this work of letter-speculation, Saadya responded to mythical and mystical
trends in tenth-century Judaism, endeavoring to recast this foundational mystical
text as a work of rational philosophy. The present article argues that Saadya was
also responding to the intellectual challenge of his broader environment, stretching
beyond the Jewish community. In some circles in the Islamicate world, letterspeculations,
often associated with the sciences of the occult, were presented in
this period as the height of philosophy. In particular, al-Tawḥīdī’s account of the
Pure Brethren and Ibn Masarra’s Book on the Properties of Letters demonstrate
the relevance of these trends in Saadya’s immediate geographic and intellectual
environment.